Agricultural combines are widely available machines which enormously speed the processes of harvesting, threshing and cleaning of all types of grains. By minimizing the labor required for harvesting, combines have contributed to the dramatic increase in availability and decrease in price of grains.
The combine machine traverses the field of grain in swathes which cover the area of the ripened crop. As it travels, the combine brings grain into its forward end and feeds it to a separating apparatus or thresher which threshes the grain, separating grain and grain heads from stalks, straw, dirt and other undesirable materials. An example of an axial flow rotor for threshing of the grain may be seen in U.S. Pat. No. 5,125,871, issued Jun. 30, 1992, to the same inventor as the present application. The present invention concerns the succeeding processing stage: the chaffing of the grain.
After passing through the threshing stage, the grain is theoretically perfectly threshed. In reality, however, while the separating apparatus is efficient, some chaff, unthreshed grain, other materials, stems, and/or straw remains intermixed with the grain and further steps of threshing, separating and cleaning are normally required.
The cleaning section of a conventional combine is located to receive grain and other material expelled from the separating apparatus. A typical cleaning section includes a chaffer and a sieve mounted so as to move back and forth reciprocally and a fan which produces a flow of air directed through the sieve and chaffer. The sieve is usually mounted below the chaffer, although it important to note that some combines have several layers of sieves and chaffers, or several in sequence. In theory, the chaffer blows the chaff and other “materials other than grain” (“MOG”) out of the stream of grain before the sieve sifts it. Reciprocation of the chaffer and sieve facilitates arrangement of the grain and other materials into a crop layer or mat on top of the chaffer. Separation of the crop material is largely facilitated by the air from the fan flowing upwardly through the passages between the louvered sieve and chaffer. Prior art chaffers/sieves include a series of adjacent louvers. A series of transverse elongated openings or passages are defined between the adjacent louvers to grade the material by density and size. Smaller, denser kernels of grain are allowed to fall through the openings despite the airflow upwards therefrom, after which they fall through the sieve mounted below the chaffer, whereas larger pieces of materials are blown or vibrated rearward in the airflow and off of the chaffer and sieve. The light material blown off the chaffer is discharged from the combine entirely, while heavier unthreshed heads of the crop still having grain is too heavy to blow and thus is moved off of the rear of the sieve, from where it is returned by the tailings system to the separating apparatus for rethreshing. Finally, there is larger MOG which is carried over the end of the chaffer and falls or blows away from there.
Thus four categories of material are created: first, the grain, which falls through the chaffer/sieve for storage, second unthreshed material which is sent back for rethreshing, and third chaff, which is blown entirely clear. Fourth, the larger material other than grain is carried off the end of the rethreshing louvers of the chaffer. To allow use of a single chaffer for grain crops of different sizes, the louvers may be adjusted in rotation, thus altering the spacing between the louvers and the characteristics of the air-flow/air-blast through them.
The proper opening between the louvers is necessary for efficient operation of the combine's chaffer. If the openings are too large, straw and other material ends up falling between them with the grain, contaminating the grain. On the other hand, if the louvers are adjusted to have openings which are too small, the individual grain requires a longer average time before finding a hole of sufficient size to pass through, thus causing a buildup of the grain, thus causing an unpredictable diminishment of the air flow, thus reducing both the speed and the efficiency of operation. Worse, some of the grain is carried off the back of the chaffer and if it falls through the louvers, is returned to the thresher unnecessarily, resulting in an excessive percentage of the grain being cracked, or if it is carried over the louvers ends up falling out the back of the combine and being lost. If the louvers are not evenly adjusted the grain may not receive uniform treatment, and in some areas, the MOG may fall through the chaffer while in others, even grain is blown away.
One particular issue is that the husk surrounding the grain may cling tightly to the grain, especially in a wheat crop, resulting in “white caps”: kernels slightly larger than the norm having husk still attached. Adjusting chaffers to use only size in a sifting or filtering apparatus to successfully reject the white caps while accepting the only slightly smaller grains which are fully threshed is a difficult process. The size difference between the chaffed and unchaffed grains can be minute: in wheat, the size difference may be as small as 5/1000 of an inch.
An example of prior art that shows a commonly used louvered system is U.S. Pat. No. 4,511,466, issued Apr. 16, 1985 to Jones et al for “Chaffer Slat”. This clearly shows that the grain flow must make a turn in flow direction in order to advance to the clean grain collection system, this turn may be anywhere from 90 degrees to almost 180 degrees, depending upon circumstances. The grain density is greater than that of the chaff, and the grain has more inertia than does the chaff, and this inertia must be overcome in making the turn. Also, in order for the grain to fall through a louver chaffer it must rely on gravity to drop between the louvers and penetrate the blast of air passing in the exact opposite direction. As can be easily appreciated there is a conflict at this point: a powerful blast of air is needed to float the chaff above the chaffer and out the back end of the combine, but the blast must not be so strong as to prevent the grain (which is being driven backwards across the chaffer) from making its turn and falling against that air blast through the louvers to the clean grain collection system. It is also worth noting that while the grain flow path pictured in FIG. 1 of the '466 patent is depicted to closely follow the underside of each louver, in fact gravity and the reciprocating motion of the chaffer causes the grain to actually land upon the top side of the following louver. However, this contact with the topside of the following louver supports the grain and diminishes the effect of gravity in moving the grain downwards against the blast of air. In addition, the MOG tends to comprise a mixture which may include straight stalks of various lengths. With large numbers of such stalks continuously fluttering and twirling in the air blast, it is inevitable that some number of them randomly end up aligned parallel to the air blast. They can then fall with great ease straight into the air blast. The slats pictured by the '466 patent are unlikely to catch and filter out such stalks as the slats are themselves aligned parallel to the airflow, and thus a certain percentage of stalks can simply fall straight through the chaffer to contaminate the grain. One final problem with such devices is that the reciprocating motion of the chaffer/sieve combination tends to “stuff” the lighter, less inertia driven material, (chaff, and other materials other than grain) into the slanted louver openings, contributing to the problem of fouling of the chaffer/sieve.
In such a louver or air foil chaffer system reliance for filtration is on the size of the openings, but in any given crop, the grain varies in size by as much as 100%. The openings of chaffers and sieves must be set wide enough to allow the largest individual grains of the crop to pass through. The opening is then wider than necessary for the smaller grains of the same crop. Any of the smaller grains that have attached husks (“white caps”) will pass through and contaminate the clean grain in the collection system. However, it is obvious that as the louvers are adjusted, the angle of the air blast is altered, the speed of the air blast is changed, the amount of support offered to the grains as they slide down the louvers is altered, and numerous other changes occur.
To illustrate the complexity of the mechanics involved, consider the case in which the louvers are narrowed from a fairly wide open configuration which was previously selected to allow a relatively large grained crop to pass there through. The narrowing of the louvers does allow them to function as screens or filters for a smaller size of crop. However, the smaller openings result in an air blast which is potentially more powerful, despite the fact that a smaller and lighter grain must now fight it's way downwards against this blast. The louvers' relatively flat angle means that the louver's top surfaces offer to the smaller grains a greater degree of support, thus reducing the pull of gravity to overcome the air blast. The fan speed must thus be adjusted to attempt to compensate not only for the smaller crop but also for the unpredictable effects of the louvers on that crop. And the new lower angle of the air blast will tend to move the mat of grain and chaff backwards faster.
In systems commercially available, the construction of the chaffer is extremely light: thin metal louvers, supports of light construction, and moving parts having fairly generous tolerances. In addition linkages necessary to actuate the multiple slats must run from the back of the chaffer (where the operator may have access) to the front. The combined effect is to produce an uncertain control response. The loose linkages, multiplied over the length of the chaffer, may result in the louver adjustment at the front end being very different from the louver adjustment at the back end, where the operator can easily see it. Individual slats may be warped by fatigue or bent by MOG falling onto them from the separator. In some commercially available systems, the length of the chaffer is divided up into multiple zones, each having a separate control system, in an attempt to deal with these problems.
The sieve below the chaffer also has unpredictable effects on the chaffer's efficiency and capacity. When filtering small seeds the angle of the louver is set as low as possible to allow the small seeds to pass into the clean grain collection system and prevent even slightly larger material other than grain from contaminating the collected clean grain. But the resulting restriction by the sieve of the air flow upwards to the chaffer starves the chaffer of needed air to function at a high capacity. To prevent overloading of the air starved chaffer, the operator must in turn slow the ground speed of the combine (thus decreasing the intake rate of the crop) or increase the speed of the cleaning fan to supply adequate air to the chaffer. Failure to do either will result in an overload condition on the top of the chaffer as is plugs with a mat of crop material. But increasing the fan speed, as discussed elsewhere, results in an undesirable loss of grain and also undesirable rethreshing of grain. Reducing ground speed and the rate of crop intake means that harvesting requires more time, which not only increases grain production cost but increases the chance that intervening events (time and weather, for example) may cause loss of a portion of the crop.
The reciprocating motion of the chaffer will also tend to move the mat of crop material (chaff, straw, stalks, and a percentage of grain) atop the chaffer rearwards out the discharge of the combine and waste whatever grain is mixed into the mat. If the operator attempts to prevent chaffer overload by increasing the fan output instead of reducing the ground speed of the combine, the sieve is over-driven with air and the grain is hit with a blast of air strong enough to blow into the tailings return auger and is needlessly rethreshed. As mentioned elsewhere, rethreshing of clean grain results in cracking and adds to the incoming crop from the harvester. When high levels of clean grain is returned to the thresher the ground speed of the combine must be reduced to prevent overload of the separator.
Other examples of such prior art combine chaffers include U.S. Pat. No. 5,041,059 issued on Aug. 20, 1991, to Ricketts et al, for “Cleaning System for a Combine” and U.S. Pat. No. 6,053,812 issued on Apr. 25, 2000, to Loewen et al for “Sieve Construction for a Combine Harvester”. In the '059 patent, a series of openings 88 are designed to allow grain to fall through louvers 62. However, since the louvers 62 have a gap between them, “allowing clean grain to fall through the sieve” (column 7, lines 14,15), materials larger than openings 88 may penetrate the chaffer of the '059 reference. Having gaps witch allow the “clean grain” to fall through the “sieve” (the chaffer, despite the difference in naming convention) is both a drawback of the '059 patent and a distinction between that patent and the present invention.
A reference of interest is U.S. Pat. No. 5,176,574, issued on Jan. 5, 1993 to Matousek et al for “Combine Cleaning System”. In the '574 patent, numerous one dimensional jets or passages in an “air foil” section of the chaffer themselves function as the holes of a screen. As shown in FIG. 5 (the representative diagram), the jets 88 are aligned in parallel rows. However, as stated in column 3, lines 7–9, and other places in the reference, the passages provide granular sizing or sorting capability. While it appears at first glance of FIG. 1 that there is a separate sieve section aft of the air foil section, FIG. 2 shows that the section extending rearwards of the air foil section is used for larger materials which are being sent back for rethreshing: this section of the chaffer overhangs return auger 52, which structure returns unthreshed materials to the threshing stage. This same point is made in column 3, lines 42–47, “ . . . materials passing through the slat section get recirculated to the threshing apparatus.” It is worth commenting that if the “airfoils” of this reference were to be interspersed among the slats, or vice-versa, the larger materials such as chaff, white caps or unthreshed heads of the grain plants, all requiring rethreshing, would not get rethreshed and would instead get mixed with the cleaned grain. It is also worth commenting that both the air foil/sieve holes and the gaps between the slats are located on the forward side of the troughs in which the airfoils sit, and that the airfoil openings 88 would continue to function as a sieve themselves no matter how the '574 reference is rearranged, as that structure and purpose is repeatedly taught in the reference, as pointed out above.
In general, the goals of combine chaffer designs are to first, allow a high capacity chaffing rate, that is to allow a high flow rate of partially threshed materials into and through the chaffer. This is of importance because the chaffing rate tends to be limiting factor in combine operation speed: increasing the chaffing capacity rate allows an immediate increase in combine operation. Second the chaffer must work efficiently to separate the grain from the chaff. High capacity of operations means little if the market quality of the grain is degraded substantially by the presence of excess chaff. These two goals may conflict.
In functional terms, turning up the air blast allows faster operation of the chaffer, up to that point when the air blast merely causes grain to be blown out the back of the combine with the chaff. This in turn leads to the observation that two separate operations are occurring in the chaffer: one operation is that grain is being separated, allowed to fall through the sieve, and collected. The other operation is that chaff is being blown backwards over the sieve and eventually out the back of the combine. (A third operation, alluded to earlier, is that unthreshed heads of grain are being collected for rethreshing.)
Another more practical problem with known chaffer designs is that of access to the chaffers and/or sieves, as well as adjustment, replacement, and cleaning. The combine has evolved into a complex machine with attachments such as grain loss monitors, chaff spreaders and straw choppers located at or near the discharge opening of the combine. These extra attachments make access to the chaffer difficult and requiring extensive time consuming disassembly to remove the chaffer and sieve. Thus whenever the chaffer must be changed, cleaned, adjusted or for any other routine maintenance, a good deal of effort is involved. In fact, the chaffer is normally only accessed from the rear, and the weight of any material clogging the chaffer, plus the weight of the chaffer and frame, plus the fact of access to one end only, all conspire to make pulling or adjusting the chaffer/sieve a tedious and difficult two person operation.